Trying to bind a C library

[lumi]

Hello,

I am trying to bind a C library and I am having trouble with forward declaration.
This is the C code:

Code: C  [Select][+][-]

1. // Forward declaration
2. struct StructA;
3.  
4. typedef void (*FunctionA)(const char* name, struct StructA result);
5.  
6. typedef struct StructA {
7.   FunctionA onComplete;
8. }
9.  

I'm a bit clueless on how to solve this cyclic dependency

Thank you! 

[marcov]

The only forward definitions are for pointer and class instances (which are also pointers). So I don't think this is possible.

The easiest solution is to define oncomplete as a pointer, and then cast it to a procedure variable on use.

If you use it really a lot, you can define a record helper that returns a property that does the cast?

[lumi]

I see, thanks! I will try it with a pointer and see how it goes. I think the library uses the function pointer as a callback

I managed to finish the bindings but when I run a simple test with it I get an Application error 0xc00007b(The application was unable to start correctly), and a 123 exit code in fp ide. Is it a problem with the DLL that I supplied?

[howardpc]

That error might indicate a 32-bit/64-bit mismatch between dll and executable.

[Zvoni]

Hello,

I am trying to bind a C library and I am having trouble with forward declaration.
This is the C code:

Code: C  [Select][+][-]

1. // Forward declaration
2. struct StructA;
3.  
4. typedef void (*FunctionA)(const char* name, struct StructA result);
5.  
6. typedef struct StructA {
7.   FunctionA onComplete;
8. }
9.  

I'm a bit clueless on how to solve this cyclic dependency

Thank you! 

I'd actually be very surprised, if The Function actually really uses the struct instead of a Pointer

would have expected

Code: [Select]

typedef void (*FunctionA)(const char* name, StructA* result);


[lumi]

Hello,

I am trying to bind a C library and I am having trouble with forward declaration.
This is the C code:

Code: C  [Select][+][-]

1. // Forward declaration
2. struct StructA;
3.  
4. typedef void (*FunctionA)(const char* name, struct StructA result);
5.  
6. typedef struct StructA {
7.   FunctionA onComplete;
8. }
9.  

I'm a bit clueless on how to solve this cyclic dependency

Thank you! 

I'd actually be very surprised, if The Function actually really uses the struct instead of a Pointer

would have expected

Code: [Select]

typedef void (*FunctionA)(const char* name, StructA* result);


This is the source code from the header of the lib:

Code: C  [Select][+][-]

1. // Forward declare
2. struct WrenLoadModuleResult;
3.  
4. // Called after loadModuleFn is called for module [name]. The original returned result
5. // is handed back to you in this callback, so that you can free memory if appropriate.
6. typedef void (*WrenLoadModuleCompleteFn)(WrenVM* vm, const char* name, struct WrenLoadModuleResult result);
7.  
8. // The result of a loadModuleFn call.
9. // [source] is the source code for the module, or NULL if the module is not found.
10. // [onComplete] an optional callback that will be called once Wren is done with the result.
11. typedef struct WrenLoadModuleResult
12. {
13.   const char* source;
14.   WrenLoadModuleCompleteFn onComplete;
15.   void* userData;
16. } WrenLoadModuleResult;
17.  

I thought the same too, that it doesn't really make sense that it is not a pointer.

Edit:

That error might indicate a 32-bit/64-bit mismatch between dll and executable.

Can you compile 64bit executable with freepascal?

[MarkMLl]

I thought the same too, that it doesn't really make sense that it is not a pointer.

If that struct really doesn't contain anything but a reference to a function, is it being optimised away so that in effect it is a pointer?

MarkMLl

[Zvoni]

I thought the same too, that it doesn't really make sense that it is not a pointer.

If that struct really doesn't contain anything but a reference to a function, is it being optimised away so that in effect it is a pointer?

MarkMLl

Don't think so, since that struct contains 3 "Fields", albeit all three are pointers.

[MarkMLl]

Don't think so, since that struct contains 3 "Fields", albeit all three are pointers.

I was looking at the original struct from OP. I agree that his more comprehensive example wouldn't optimise like I suggested.

The perils of people not posting the exact code that was giving them problems...

MarkMLl

[lumi]

The perils of people not posting the exact code that was giving them problems...

Yes, I am sorry, I thought it would be more straight forward with "dumbed down" c code.

I tried multiple settings to compile the Wren library, but I still get the errors. I wanted to make sure that I can load .dll that have been built with VS (I also tried to load a .lib but apparently it isn't supported?)

[MarkMLl]

The perils of people not posting the exact code that was giving them problems...

Yes, I am sorry, I thought it would be more straight forward with "dumbed down" c code.

No problem :-)

I tried multiple settings to compile the Wren library, but I still get the errors. I wanted to make sure that I can load .dll that have been built with VS (I also tried to load a .lib but apparently it isn't supported?)

The ultimate arbiter will be looking at the machine code associated with the specific entry and return points in the DLL. But I admit that I'm extremely rusty at this sort of thing... I've not had to do it for 20+ years and the available tools have changed a lot since then.

What do you mean that .lib isn't supported? Do you mean that the library you're trying to load isn't available in a .lib for static linkage or that FPC can't do static linkage (the latter is definitely wrong).

MarkMLl

[lumi]

What do you mean that .lib isn't supported? Do you mean that the library you're trying to load isn't available in a .lib for static linkage or that FPC can't do static linkage (the latter is definitely wrong).

What I meant was, that I tried following the binding guide (https://github.com/williamhunter/pascal-bindings-for-c) and added

Code: Pascal  [Select][+][-]

1. {$linklib wren.lib}

at the top of my binding and I got a compile error :

Code: [Select]

Invalid DLL, Dos Header invalid

[skalogryz]

if you're using Borland C or MSVC it might not work.
You want to use gcc compiler instead. or maybe even clang.

Gcc from mingw package is the usual choice.

Please note that LINKLIB is used for STATIC linking.

If you're compiling a .dll, then any C/C++ compiler would work, but you should not be using $linklib.
Instead you should declare a function as external and specify the dll name in the external reference.

[lumi]

Let me rephrase cause I might be expressing myself poorly.
I first tried to dynamically link the .dll (compiled with msvc) with external references.
And then I tried to statically link it with a .lib with $linklib  that I compiled using MSVC.

Both failed with different error messages, probably cause I messed up somewhere!

I'm gonna leave the source too so it's easier to spot the mistakes. (it's not terribly long, but I'm not well versed enough with pascal yet)
Here is what I have currently for the binding(dynamic linking): https://gist.github.com/lumi-c/0a84df98685460d43c281fa508e86b25
And here is the header of the source code: https://github.com/wren-lang/wren/blob/main/src/include/wren.h

[skalogryz]

And then I tried to statically link it with a .lib with $linklib  that I compiled using MSVC.

Static linking with MSVC out-of-thebox compiled librariry won't work.
Maybe there are some settings in MSVC to compile gcc compatible libraries, but I doubt.
So let's forget this option

tried to dynamically link the .dll (compiled with msvc) with external references.
...
different error messages, probably cause I messed up somewhere!

what compilation error did you get when tied to use the .dll?